Note: stock has a hole already drilled way off center. When
using a steady rest, the stock wants to "walk" out
of the chuck, so a center was needed. I had a piece of aluminum
between the dead center and the stock as I could not use the
hole.

I would also have drilled and tapped it first but waited
until later.

Note: you don't want any radius in the corner. That will cause
the nut to try an pry the T-slot apart and possibly crack it.
Easisest is to move the bit farther into the corner. In this
case it was ground off later and was a pain to do.

Part near completely parted off. I did start a part groove
sightly behind then did the full cut at the desired thickness.
That made it a bit easier to get cutting fluid in and chips somewhere
to go.

Test fit for thickness of disc. Flipped over, the stub
fits in the slot. Note stud is too long at this point.

I mounted the part in the 3-jaw and faced the stud until
the height was just less than the upper part of the T-slot. You
do not want it touching the tool post.

Then I bored a hole using a milling bit. I had to use a mill
bit as the hole in the stock was about 0.100" off center.

Picture is tapping the nut for the 7/16 bolt used on the tool
post. Note, I'm using the live center to keep the tap straight.

Tapping was done by hand by locking the spindle (back gear
with pin in) and turning by hand while keeping the tailstock
snug.

Last step is completely manual. Clamp in vice and "cut
the ears off". ;)

I roughly scribed 0.2" outside the stud and cut with
a hacksaw. It was snug so I did a bit of grinding with a die
grinder and then a file to fine tune.